Process for refining crude resin for resist

ABSTRACT

A process for refining a crude resin for a resist is provided, which is capable of effectively removing by-products such as polymers and oligomers contained within the crude resin. The process provides a refining process for the crude resin of a resist resin (A) used in a photoresist composition comprising at least the resist resin (A) and an acide generator (B) dissolved in a first organic solvent (C1), wherein if the concentration of the component (A) in the photoresist composition is labeled X, and the crude resin concentration of the component (A) in a crude resin solution comprising the crude resin of the component (A) dissolved in a second organic solvent (C2) is labeled Y, then (i) the crude resin solution is prepared so that Y is smaller than X, and (ii) the crude resin solution is subsequently filtered.

TECHNICAL FIELD

The present invention relates to a process for refining a crude resinfor a resist, a resist resin produced by such a refining process, aprocess for producing a photoresist composition using such a resistresin, and a photoresist composition comprising such a resist resin.

BACKGROUND ART

Typical examples of resist resins used during the production ofelectronic devices such as semiconductor elements, liquid crystalelements and magnetic heads and the like include polyhydroxystyrenebased resins (such as resins in which a portion of the hydroxyl groupsare protected with acid dissociable, dissolution inhibiting groups,copolymers of hydroxystyrene units and styrene units, and copolymers ofhydroxystyrene units and (meth)acrylate esters) in the case of KrFresist resins, and (meth)acrylate ester copolymer based resins in thecase of ArF resist resins.

Examples of processes for refining these types of resist resins includethe processes disclosed in the patent reference 1 listed below in thecase of the former type polyhydroxystyrene based resins, and theprocesses disclosed in the patent reference 2 listed below in the caseof the latter type (meth)acrylate ester copolymer based resins.

The patent reference 1 discloses a process in which the resin isdissolved in a polar solvent such as N-methylpyrrolidone and analiphatic hydrocarbon based solvent, and following phase separation theresin is extracted from the polar solvent layer, as well as a process inwhich the resin is dissolved in a lower alcohol, and is then added to apoor solvent such as water to precipitate the polymer.

The patent reference 2 discloses a process in which the resin is refinedusing an aliphatic hydrocarbon such as n-hexane, or a mixed solvent ofan aliphatic hydrocarbon and ethyl acetate.

Patent Reference 1: Japanese Unexamined Patent Application, FirstPublication No. Hei 6-289614 A

Patent Reference 2: Japanese Unexamined Patent Application, FirstPublication No. 2002-201232 A

However, when a crude resin for a resist is refined using these types ofprocesses, even if the unreacted monomer is able to be removed to someextent, the removal of by-product oligomers or low molecular weightpolymers, or polymers with a higher molecular weight than the targetedweight average molecular weight, is particularly difficult.Consequently, the use of resist resins containing these types ofby-products that are difficult to remove as components is unavoidable.

For example, when an ArF chemically amplified photoresist composition isprepared using a resin containing the aforementioned by-productoligomers or low molecular weight polymers, or by-product polymers witha higher molecular weight than the targeted weight average molecularweight, although the various characteristics such as the sensitivity,the resolution, and the resist pattern shape are satisfactory, thenumber of defects in the resist pattern following developing can becomeproblematic. These defects refer to general problems such as scum andbridging between resist patterns detected by inspecting the developedresist pattern from directly overhead using, for example, a surfacedefect inspection apparatus manufactured by KLA Tencor Corporation(brand name “KLA”).

Furthermore, during storage as a resist solution (a photoresistcomposition in solution form), problems may also develop in terms of thestorage stability as a resist solution, resulting in the development offine particles within the solution. Moreover, if these fine particlesdevelop, they can cause the type of defects described above, meaningimprovements in the storage stability as a resist solution are needed inorder to improve the level of defects.

DISCLOSURE OF INVENTION

The present invention takes the above problems associated with theconventional art into consideration, with an object of providing aprocess for refining a crude resin for a resist, which enables theeffective removal of by-product oligomers or low molecular weightpolymers, or by-product polymers with a higher molecular weight than thetargeted weight average molecular weight, contained within the resistresin, and is capable of improving the level of defects and the storagestability as a resist solution, without impairing characteristics suchas the resolution, the resist pattern shape and the sensitivity, as wellas a resist resin produced by such a refining process, a process forproducing a photoresist composition using such a resist resin, and aphotoresist composition comprising such a resist resin.

As a result of intensive investigations aimed at resolving the aboveproblems, the inventors of the present invention discovered that theabove problems could be resolved using the devices described below, andwere hence able to complete the present invention.

Namely, a first aspect of the present invention is a process forrefining a crude resin of a resist resin (A) used in a photoresistcomposition comprising at least the resist resin (A) and an acidgenerator (B) dissolved in a first organic solvent (C1), wherein if theconcentration of the above component (A) in the photoresist compositionis labeled X, and the crude resin concentration of the component (A) ina crude resin solution comprising the crude resin of the component (A)dissolved in a second organic solvent (C2) is labeled Y, then (i) thecrude resin solution is prepared so that Y is smaller than X, and (ii)the crude resin solution is subsequently filtered.

A second aspect of the present invention is a resist resin produced bythe above refining process.

A third aspect of the present invention is a process for producing aphotoresist composition using an aforementioned resist resin.

A fourth aspect of the present invention is a photoresist compositioncomprising an aforementioned resist resin.

The term “(meth)acrylic acid” refers to either one of, or both,methacrylic acid and acrylic acid. The term “structural unit” refers toa monomer unit that contributes to the formation of a polymer. The term“lactone unit” refers to a group in which one hydrogen atom has beenremoved from a monocyclic or polycyclic lactone. Furthermore, the term“crude resin” describes the unrefined state immediately followingpolymerization of a resin.

According to the present invention, there are provided a process forrefining a crude resin for a resist that enables the effective removalof by-products such as polymers and oligomers contained within theresist resin, as well as a resist resin produced by such a refiningprocess, and a process for producing a chemically amplified photoresistcomposition using such a resist resin.

BEST MODE FOR CARRYING OUT THE INVENTION

As follows is a sequential description of one example of a process forrefining a crude resin for a resist according to the present invention.

First, a crude resin is prepared by a typical polymerization reaction.In other words, at least one monomer that generates the structural unitsof the target resin is first dissolved in a typical polymerizationsolvent. Examples of typical polymerization solvents includetetrahydrofran, dioxane, and methyl ethyl ketone. Next, a knownpolymerization initiator such as azobisisobutyronitrile is added to thesolution, and the polymerization is conducted by heating, preferably at50 to 80° C., for a period of 2 to 6 hours.

Next, following completion of the polymerization reaction, the reactionliquid containing the dissolved product resin is poured into a washingsolvent. As this washing solvent, for example, a polar solvent or ahydrophobic solvent can be used.

Polar solvents are solvents that contain a polar group such as ahydroxyl group, and display comparatively high hydrophilicity. Examplesof such polar solvents include alcohols of 1 to 4 carbon atoms such asmethanol, ethanol, n-propanol, iso-propanol, n-butanol, andtert-butanol. Of these, methanol, ethanol and iso-propanol areparticularly preferred.

Hydrophobic solvents are solvents that do not contain polar groups suchas hydroxyl groups, and display comparatively high hydrophobicity.Examples of hydrophobic solvents include the aliphatic hydrocarbons.Hydrocarbons of 5 to 11 carbon atoms are preferred, and specificexamples include pentane, 2-methylbutane, n-hexane, 2-methylpentane,2,2-dibutylbutane, 2,3-dibutylbutane, n-heptane, n-octane, isooctane,2,2,3-trimethylpentane, n-nonane, 2,2,5-trimethylhexane, n-decane andn-dodecane, and of these, n-hexane and n-heptane are particularlypreferred.

The quantity added of the washing solvent is preferably equivalent to atleast 2-fold the mass, and preferably from 4 to 5-fold the mass of thepolymerization solvent, as such quantities enable better removal ofimpurities such as the unreacted monomer. Following addition of thewashing solvent, the mixture is preferably stirred or shaken at 10 to40° C., and preferably from 20 to 30° C., for a period of 10 to 60minutes, and preferably from 25 to 35 minutes, thereby precipitating thecrude resin as a solid. The crude resin is obtained by filtering offthis precipitated solid.

This washing step using the washing solvent can also be repeated ifnecessary. In other words, the resin obtained following the abovewashing operation can be redissolved in a polymerization solvent such astetrahydrofuran, and the operation of pouring the solution into thewashing solvent and then filtering off the precipitated resin can berepeated.

By washing the crude resin produced by the polymerization reaction witha washing solvent, in the manner described above, the majority of theunreacted monomer from the polymerization reaction can be dissolved inthe washing solvent and removed. However, the removal of by-productoligomers or low molecular weight polymers from the polymerizationreaction, or by-product polymers with a higher molecular weight than thetargeted weight average molecular weight, and particularlycompositionally biased polymers or oligomers with a high proportion of aspecific structural unit, is difficult.

By employing a refining process of the present invention, and inparticular the characteristic feature of the present invention whereinif the concentration of the component (A) in the photoresist compositionis labeled X, and the crude resin concentration of the component (A) ina crude resin solution comprising the crude resin of the component (A)dissolved in the second organic solvent (C2) is labeled Y, then (i) thecrude resin solution is prepared so that Y is smaller than X, and (ii)the crude resin solution is subsequently filtered, the types ofby-products described above can be effectively removed.

There are no particular restrictions on the first organic solvent (C1)and the second organic solvent (C2) used in the present invention,provided they are capable of dissolving the resist resin, and eitherone, or two or more conventional resist solvents can be used.

Examples of the above organic solvents (C1) and (C2) include ketonessuch as acetone, methyl ethyl ketone, cyclohexanone, methyl isoamylketone and 2-heptanone; polyhydric alcohols and derivatives thereof suchas ethylene glycol, ethylene glycol monoacetate, diethylene glycol,diethylene glycol monoacetate, propylene glycol, propylene glycolmonoacetate, dipropylene glycol, or the monomethyl ether, monoethylether, monopropyl ether, monobutyl ether or monophenyl ether ofdipropylene glycol monoacetate; cyclic ethers such as dioxane; andesters such as methyl lactate, ethyl lactate, methyl acetate, ethylacetate, butyl acetate, methyl pyruvate, ethyl pyruvate, methylmethoxypropionate, and ethyl ethoxypropionate. These organic solventscan be used singularly, or as a mixed solvent of two or more differentsolvents. Furthermore, as (C1) and (C2), either the same solvent, ordifferent solvents may be used, although from the viewpoint ofefficiency during the resist composition preparation, use of the samesolvent is preferred.

Of these solvents, propylene glycol monomethyl ether acetate (hereafterabbreviated as PGMEA) and ethyl lactate (hereafter abbreviated as EL)are the most widely used due to the safety they offer as resistsolvents, and are consequently preferred.

There are no particular restrictions on the resist resin (A) and theacid generator (B) used in the photoresist composition, and conventionalmaterials are suitable. Furthermore, the expression “at least” meansthat other typically employed optional components may be included in thephotoresist composition in addition to the aforementioned component (A)and component (B).

The concentration X of the component (A) in the photoresist compositionis the concentration of the resist resin (A) in the photoresistcomposition in solution form, produced by dissolving at least therefined component (A) and the component (B) in the component (C1).

There are no particular restrictions on the resist resin concentrationwithin a photoresist composition suitable for use with an exposuresource with a wavelength of no more than 248 nm (such as KrF, ArF or F₂excimer laser light, or other radiation such as extreme UV, EB (electronbeam) or X-ray radiation), although the composition is preferablyprepared with a resin concentration of 5 to 25% by weight, and even morepreferably from 7 to 20% by weight. If the concentration falls outsidethis range, then forming a film thickness that is appropriate for theexposure source may become difficult.

The crude resin concentration Y of the component (A) in a crude resinsolution comprising the crude resin of the component (A) dissolved inthe second organic solvent (C2) is, as the description suggests, theconcentration of the component (A) in the crude resin solutioncomprising the unrefined crude resin of the component (A) dissolved in(C2).

The refining process of the present invention requires that (i) thecrude resin solution is prepared so that Y is smaller than X, and (ii)the crude resin solution is subsequently filtered.

The solution is prepared so that as described above, Y is smaller thanX, although there are no particular restrictions on the value of Y. Theactual value of Y need only be less than the actual value of X selectedfrom the aforementioned concentration range of 5 to 25% by weight, andeven more preferably from 7 to 20% by weight Y values within a rangefrom 2 to 10% by weight are even more preferred, and values from 6 to10% by weight are the most preferred. By first preparing a solution ofthe crude resist resin that is more dilute than the concentration of theresist resin in the final photoresist composition, by-products can beprecipitated out of this dilute resist solution.

Subsequently, the crude resin solution is filtered.

Filtering of the crude resin solution can be conducted usingconventional methods, although filtration through a filter with afiltration membrane is preferred. There are no particular restrictionson the material for the filtration membrane, which can be any materialtypically used in the filtration of photoresist compositions, andspecific examples include fluororesins such as PTFE(polytetrafluoroethylene); polyolefin resins such as polypropylene andpolyethylene; and polyamide resin such as nylon 6 and nylon 66. Ofthese, polyethylene, polypropylene, nylon 66 and nylon 6 are preferred,as they offer superior removal of oligomers and low molecular weightpolymers, or polymers with a higher molecular weight than the targetedweight average molecular weight, which are produced as by-products inthe polymerization reaction, and as a result provide a superior defectreduction effect and superior storage stability as a resist solution.

The pore size of the above filter is preferably within a range from 0.02to 0.1 μm, and even more preferably from 0.02 to 0.05 μm, as such sizesoffer the most effective removal of the above by-products. If the filterpore size is less than 0.02 μm, then the filtration speed becomes overlyslow, and there is a danger of an undesirable fall in productivity. Incontrast if the pore size exceeds 0.1 μm, there is a danger that theoligomers and low molecular weight polymers, or polymers with a highermolecular weight than the targeted weight average molecular weight,produced as by-products in the polymerization reaction will not beeffectively removed.

Furthermore, passing the crude resist resin solution described abovethrough a two-stage filter using filtration membranes offers even moreeffective removal of the polymer and oligomer by-products, and resultsin an even more superior defect reduction effect and even better storagestability as a resist solution, and is consequently the most preferredoption. In one specific example of the filtering process, the dilutecrude resin solution is filtered through a nylon filter as the firstfiltration step, and the resulting filtrate is then filtered through apolypropylene filter as the second filtration step. A polyethylenefilter could also be used in this second filtration step. Specificexamples of the above nylon filter include ULTIPORE N66 (brand name:manufactured by Nihon Pall Ltd.) which is manufactured from NYLON 66(brand name), and the ULTIPLEAT P-NYLON FILTER (brand name: manufacturedby Nihon Pall Ltd., pore size 0.04 μm) which is also manufactured fromNYLON 66 (brand name).

By removing a predetermined quantity of solvent from the filtratecontaining the refined target resin, and adjusting the concentration ofthe resist resin within the photoresist composition to the desiredlevel, the filtrate can be used, as is, as the resist resin solution forthe photoresist, which is the preferred option. The photoresistcomposition can then be produced efficiently by simply adding the acidgenerator component and any other optional components to the resistsolution. Alternatively, the solvent could also be removed completely,and the resulting solid resin then used in the subsequent production ofthe photoresist composition.

In a process for refining a crude resin for a resist according to thepresent invention, the order in which the aforementioned washing processusing a washing solvent, and the aforementioned steps (i) and (ii) areperformed may also be reversed.

Carrying out the above washing process step using the washing solventfirst, to produce a solid crude resin from which monomers and the likehave been removed, and then conducting the aforementioned steps (i) and(ii) is preferred as it results in a more effective removal ofby-products such as oligomers and polymers.

The process for refining a crude resin for a resist according to thepresent invention is used for refining resins used in photoresistcompositions. There are no particular restrictions on these resistresins, and suitable examples include hydroxystyrene based resins and(meth)acrylate based resins, although resins produced by a radicalpolymerization reaction are preferred. In addition, the presentinvention is also suited to the production of resins that can be used inchemically amplified photoresist compositions, and particularly resinscontaining structural units derived from (meth)acrylate esters. Examplesof resins containing structural units derived from (meth)acrylate estersinclude, for example, the resin components of photoresist compositionssuitable for use with ArF excimer lasers.

Specifically, the refining process of the present invention ispreferably used in the production of resins containing the structuralunits (a1) described below.

(a1) Structural units derived from a (meth)acrylate ester containing ahydrophilic site (hereafter referred to as (a1) units).

(a1) Units:

An (a1) unit is a structural unit containing a hydrophilic site on theester side chain section of a (meth)acrylate ester. There are noparticular restrictions on the hydrophilic site, although lactone unitsare particularly preferred. In the lactone unit, the ring containing the—O—C(O)— structure is counted as the first ring. Accordingly, the casein which the only ring structure is the ring containing the —O—C(O)—structure is referred to as a monocyclic group, and groups containingalso other ring structures are described as polycyclic groups regardlessof the structure of the other rings.

Specific examples of the (a1) unit include monocyclic groups in whichone hydrogen atom has been removed from γ-butyrolactone, and polycyclicgroups in which one hydrogen atom has been removed from a lactonecontaining bicycloalkane.

Specifically, the structural units represented by the structuralformulas (I) to (IV) shown below are preferred.

(wherein, R represents a hydrogen atom or a methyl group, and mrepresents either 0 or 1)

(wherein, R represents a hydrogen atom or a methyl group)

(wherein, R represents a hydrogen atom or a methyl group)

(wherein, R represents a hydrogen atom or a methyl group)

The above structural units (a1) preferably account for 20 to 60 mol %,and even more preferably from 30 to 50 mol % of the total of all thestructural units within the resin, as such proportions result insuperior resolution.

In those cases in which the resist resin to which the refining processof the present invention is applied is a resin comprising the (a1) unitsdescribed above, the raw material monomers are preferably monomerscontaining a lactone unit with a comparatively high level ofhydrophilicity. When production of a resin is conducted using such amonomer, oligomers and low molecular weight polymers comprising a largeproportion of structural units containing a lactone unit, or polymerscomprising a large proportion of structural units containing a lactoneunit and with a higher molecular weight than the targeted weight averagemolecular weight are generated as by-products. Because these highlyhydrophilic oligomers and polymers and the like typically display poorsolubility in resist solvents, application of the production process ofthe present invention in these cases is particularly desirable. Byfiltering a dilute resin solution, the highly hydrophilic oligomers andpolymers can be removed effectively. This enables a reduction in thelevel of defects, and an improvement in the storage stability of theresin, both of which cause problems in chemically amplifiedphotoresists.

A resist resin to which the refining process of the present invention isapplied preferably comprises structural units (a) described below.

(a2) Structural units derived from a (meth)acrylate ester containing ahydrophobic group (hereafter referred to as (a2) units).

(a2) Units:

The hydrophobic group within the (a2) unit refers to a highlyhydrophobic hydrocarbon group containing at least 6 carbon atoms, andpreferably 10 or more carbon atoms, contained within the ester sectionof the (meth)acrylate ester. The hydrocarbon group may be either achain-type or a cyclic hydrocarbon group, and specific examples includea hydrophobic group containing a tertiary alkyl group, a monocyclicgroup, or a polycyclic group. Of these, aliphatic type monocyclic orpolycyclic hydrocarbon groups are preferred, and polycyclic hydrocarbongroups are particularly preferred as they result in superior resolutionand dry etching resistance.

Examples of these (a2) units include the structural units (a2-1) and(a2-2) described below.

(a2-1) Structural units derived from a (meth)acrylate ester comprisingan acid dissociable, dissolution inhibiting group containing ahydrophobic aliphatic monocyclic or polycyclic group (hereafter referredto as (a2-1) units).

(a2-2) Structural units derived from a (meth)acrylate ester comprising anon-acid dissociable group containing a hydrophobic aliphatic polycyclicgroup (hereafter referred to as (a2-2) units).

The term “non-acid dissociable” used in the description of the (a2-2)units does not mean that the group is chemically completelynon-dissociable, but rather that the level of acid dissociability islower than that of an (a2-1) unit and results in no significant resistpatterning.

(a2-1) Units:

In terms of the acid dissociable, dissolution inhibiting groupcontaining a monocyclic or polycyclic group that is used as thehydrophobic group in the (a2-1) unit, suitable examples of the aliphaticmonocyclic group include groups in which one hydrogen atom has beenremoved from a cycloalkane, and suitable examples of the aliphaticpolycyclic group include groups in which one hydrogen atom has beenremoved from a bicycloalkane, a tricycloalkane or a tetracycloalkane orthe like.

Specific examples include groups in which one hydrogen atom has beenremoved from cyclohexane in the case of an aliphatic monocyclic group,and groups in which one hydrogen atom has been removed from apolycycloalkane such as adamantane, norbornane, isobornane,tricyclodecane or tetracyclododecane in the case of an aliphaticpolycyclic group.

This polycyclic group can be appropriately selected from the multitudeof acid dissociable, dissolution inhibiting groups proposed for usewithin ArF excimer laser photoresist composition resins.

Of these groups, cyclohexyl groups, adamantyl groups, norbornyl groups,and tetracyclododecanyl groups are preferred in terms of industrialavailability.

There are no particular restrictions on the above acid dissociable,dissolution inhibiting group, providing it is a group which can be usedin a resin for a positive chemically amplified photoresist composition,and which dissociates under the action of acid, causing the resin toshift from an alkali insoluble state to an alkali soluble state.

Typically, groups in which a cyclic or a chain-type tertiary alkyl esteris formed at the carboxyl group of the (meth)acrylic acid are the mostwidely used.

Specifically, the structural unit (a2-1) is preferably at least one unitselected from a group consisting of the general formulas (V) to (VII)shown below.

(wherein, R represents a hydrogen atom or a methyl group, and R¹represents a lower alkyl group)

(wherein, R represents a hydrogen atom or a methyl group, and R² and R³each represent, independently, a lower alkyl group)

(wherein, R represents a hydrogen atom or a methyl group, and R⁴represents a tertiary alkyl group)

Within the above formula, the group R¹ is preferably a straight chain orbranched alkyl group of 1 to 5 carbon atoms, and specific examplesinclude a methyl group, ethyl group, propyl group, isopropyl group,n-butyl group, isobutyl group, tert-butyl group, pentyl group, isopentylgroup and neopentyl group. Of these, an alkyl group of at least 2 carbonatoms, and preferably from 2 to 5 carbon atoms, is preferred as itprovides an acid dissociability that is greater than the case in whichR¹ is a methyl group, and enables higher sensitivity. From an industrialviewpoint, a methyl group or an ethyl group is preferred.

The aforementioned groups R² and R³ each preferably represent,independently, a lower alkyl group of 1 to 5 carbon atoms. These typesof groups tend to display a higher acid dissociability than a2-methyl-2-adamantyl group.

Specifically, the groups R² and R³ preferably each represent,independently, the same types of straight chain or branched lower alkylgroups described above for R¹. Of these groups, the case in which R² andR³ are both methyl groups is preferred in terms of industrialavailability, and specific example of the structural unit represented bythe formula (VI) includes structural unit derived from2-(1-adamantyl)-2-propyl (meth)acrylate.

The group R⁴ represents a tertiary alkyl group such as a tert-butylgroup or a tert-amyl group, although a tert-butyl group is preferred interms of industrial availability.

Furthermore, the group —COOR⁴ may be bonded to either position 3 or 4 ofthe tetracyclododecanyl group shown in the formula, although a mixtureof both stereoisomers results, and so the bonding position cannot befurther specified. Furthermore, the carboxyl group residue of the(meth)acrylate structural unit may be bonded to either position 8 or 9,although similarly, the bonding position cannot be further specified.

The above structural units (a2-1) preferably account for 20 to 60 mol %,and even more preferably from 30 to 50 mol % of the total of all thestructural units within the resin, as such proportions result insuperior resolution.

(a2-2) Units:

(a2-2) units comprise a non-acid dissociable group containing ahydrophobic aliphatic polycyclic group.

Examples of the aliphatic polycyclic group include the same groupsdescribed above in relation to the (a2-1) units, and any of themultitude of conventional groups proposed for use within ArF excimerlaser photoresist composition resins can be used.

From the viewpoint of industrial availability, at least one of atricyclodecanyl group, an adamantyl group or a tetracyclododecanyl groupis preferred.

Specific examples of the (a2-2) unit include the units with thestructures (VIII) to (X) shown below.

(wherein, R represents a hydrogen atom or a methyl group)

(wherein, R represents a hydrogen atom or a methyl group)

(wherein, R represents a hydrogen atom or a methyl group)

The above structural units (a2-2) preferably account for 1 to 30 mol %,and even more preferably from 5 to 20 mol % of the total of all thestructural units within the resin, as such proportions result inexcellent resolution for isolated patterns through to semi densepatterns.

In those cases in which the resist resin to which the refining processof the present invention is applied is a resin comprising the (a2) unitsdescribed above, monomers containing a hydrophobic group are used as theraw material monomers. When production of a resin is conducted usingsuch monomers, highly hydrophobic oligomers and low molecular weightpolymers comprising a large proportion of structural units containing ahydrophobic group are generated as by-products. In addition, highlyhydrophobic polymers comprising a large proportion of structural unitscontaining a hydrophobic group are also generated as by-products.Because these highly hydrophobic oligomers and polymers and the liketypically display poor solubility in resist solvents, application of theproduction process of the present invention, namely filtering a dilutesolution of the resin to enable the highly hydrophobic oligomers andpolymers to be removed effectively, can be favorably employed, enablinga further improvement in the defect reduction effect.

Suitable crude resins for use with a refining process of the presentinvention preferably comprise both the aforementioned (a1) units and theaforementioned (a2) units.

Furthermore, the crude resin may also comprise another structural unit(a3) in addition to the (a1) units and (a2) units described above.

There are no particular restrictions on the (a3) unit, provided itcannot be classified as one of the above units (a1) and (a2). Forexample, structural units derived from a (meth)acrylate ester comprisinga hydroxyl group containing aliphatic polycyclic group are preferred.

The aliphatic polycyclic group may be appropriately selected from theplurality of polycyclic groups listed in the description of the abovestructural unit (a1).

Specifically, hydroxyl group containing adamantyl groups or carboxylgroup containing tetracyclododecanyl groups are preferred as thestructural unit (a3).

More specific examples include the structural units represented by thegeneral formula (XI) shown below. The (a3) units preferably account for5 to 50 mol %, and even more preferably from 10 to 40 mol % of the totalof all the structural units within the resin, as such proportions resultin a superior resist pattern shape when the resin is used as achemically amplified photoresist resin.

(wherein, R represents a hydrogen atom or a methyl group, and nrepresents an integer of 1 to 3)

In addition, a crude resin for a resist suitable for use with a refiningprocess of the present invention may comprise two types of units,namely, acrylate ester units and methacrylate ester units, andcombinations of these two units resulting in three types of crude resin,namely, resins containing only acrylate ester units, resins containingonly methacrylate ester units, and resins containing both types of units

The refining process of the present invention is particularly suited toresins containing only structural units derived from methacrylateesters, and resins containing from 20 to 70 mol % of structural unitsderived from acrylate esters, and from 30 to 80 mol % of structuralunits derived from methacrylate esters.

In addition, the latter type of resins containing structural unitsderived from acrylate esters and structural units derived frommethacrylate esters in a specific ratio are prone to the production ofoligomer and low molecular weight polymer by-products of differingpolarity, due to the difference in polarity of the structural unitsderived from acrylate esters and the structural units derived frommethacrylate esters, although these types of by-products can also beeffectively removed using a refining process of the present invention.

As follows is a description of a chemically amplified photoresistcomposition that can be readily produced using a resist resin obtainedby the refining process of the present invention described above.

This chemically amplified photoresist composition comprises (A) a resincomponent (hereafter referred to as component (A)), (B) an acidgenerator component that generates acid on exposure (hereafter referredto as component (B)), and (C1) a first organic solvent (hereafterreferred to as component (C1)). In those cases when a resist resin ofthe present invention is used as a photoresist composition, thecomponent (A) is either an alkali soluble resin or a resin that can beconverted to an alki soluble state. The former case is a so-callednegative photoresist composition, and the latter case a so-calledpositive photoresist composition.

In the case of a negative type composition, a cross linking agent isadded to the photoresist composition with the component (13). Then,during resist pattern formation, when acid is generated from thecomponent (13) by exposure, this acid acts on the cross linking agent,causing cross linking between the component (A) and the cross linkingagent, and making the composition alkali insoluble. As the cross linkingagent, either a compound with a methylol group or an alkyl etherthereof, including amino based resins such as melamine resin, urea resinor glycoluril resin is typically used. In the case of a positive typecomposition, the component (A) is an alkali insoluble resin with aso-called acid dissociable, dissolution inhibiting group, and when acidis generated from the component (B) by exposure, this acid causes theacid dissociable, dissolution inhibiting group to dissociate, making thecomponent (A) alkali soluble. In this case, the resin must comprise (a1)units and (a2-1) units.

Component (A):

As the component (A), the above types of resist resins, obtained usingthe process for refining a resist resin according to the presentinvention, are used.

There are no particular restrictions on the polystyrene equivalentweight average molecular weight of the component (A), as determined byGPC, although values within a range from 5,000 to 30,000 are preferred,and values from 8,000 to 20,000 are even more desirable.

Furthermore, the component (A) can be formed from either one, or two ormore different resins, and for example, as the component (A), one or twoor more of the above types of resins comprising units derived from(meth)acrylate esters as the principal components may be utilized, ormixtures with other conventional photoresist composition resins may alsobe utilized.

Component (B):

The component (B) can be appropriately selected from known materialsused as acid generators in conventional positive and negative chemicallyamplified resists.

Specific examples include onium salts such as diphenyliodoniumtrifluoromethanesulfonate, (4-methoxyphenyl)phenyliodoniumtrifluoromethanesulfonate, bis(p-tert-butylphenyl)iodoniumtrifluorometlanesulfonate, triphenylsulfonium trifluoromethanesulfonate,(4-methoxyphenyl)diphenylsulfonium trifluoromethanesulfonate,(4-methylphenyl)diphenylsulfonium nonafluorobutanesulfonate,(p-tert-butylphenyl)diphenylsulfonium trifluoromethanesulfonate,diphenyliodonium nonafluorobutanesulfonate,bis(p-tert-butylphenyl)iodonium nonafluorobutanesulfonate andtriphenylsulfonium nonafluorobutanesulfonate. Of these, onium salts witha fluorinated alkylsulfonate ion as the anion are preferred.

As this component (B), a single compound, or a combination of two ormore compounds may be utilized. The quantity of the component (B) istypically within a range from 0.5 to 30 parts by weight per 100 parts byweight of the component (A).

Component (C1):

The component (C1) can be any solvent capable of dissolving thecomponent (A) and the component (B) to generate a uniform solution, andthe solvent used can be one, or two or more solvents selected fromamongst known solvents used for conventional chemically amplifiedresists.

Specific examples of the solvent include ketones such as acetone, methylethyl ketone, cyclohexanone, methyl isoamyl ketone and 2-heptanone;polyhydric alcohols and derivatives thereof such as ethylene glycol,ethylene glycol monoacetate, diethylene glycol, diethylene glycolmonoacetate, propylene glycol, propylene glycol monoacetate, dipropyleneglycol, or the monomethyl ether, monoethyl ether, monopropyl ether,monobutyl ether or monophenyl ether of dipropylene glycol monoacetate;cyclic ethers such as dioxane; and esters such as methyl lactate, ethyllactate, methyl acetate, ethyl acetate, butyl acetate, methyl pyruvate,ethyl pyruvate, methyl methoxypropionate, and ethyl ethoxypropionate.These organic solvents can be used singularly, or as a mixed solvent oftwo or more different solvents.

Of these solvents, propylene glycol monomethyl ether acetate (PGMEA) andethyl lactate (EL) and the like are preferred.

The quantity of the component (Cl) is sufficient to generate aconcentration that is suitable for use as a photoresist composition, andenables application of the composition to a substrate or the like.

Other Components:

Other components may also be added to the photoresist compositionaccording to need.

For example, in order to improve the resist pattern shape and the longterm stability (post exposure stability of the latent image formed bythe pattern wise exposure of the resist layer), an amine, andparticularly a secondary lower aliphatic amine or a tertiary loweraliphatic amine, can also be added as an optional component (D).

Here, a lower aliphatic amine refers to an alkyl or alkyl alcohol amineof no more than 5 carbon atoms, and examples of these secondary andtertiary amines include trimethylamine, diethylamine, triethylamine,di-n-propylamine, tri-n-propylamine, tripentylamine, diethanolamine andtriethanolamine, and alkanolamines such as triethanolamine areparticularly preferred.

These may be used singularly, or in combinations of two or moredifferent compounds.

This amine is typically added in a quantity within a range from 0.01 to5.0 parts by weight per 100 parts by weight of the component (A).

Furthermore, in line with the objectives of preventing any deteriorationin sensitivity, and improving the resist pattern shape and the long termstability by adding the component (D), an organic carboxylic acid, or aphosphorus oxo acid or derivative thereof can also be added as anoptional component E). Either one, or both of the component (D) and thecomponent (E) can be used.

Examples of suitable organic carboxylic acids include malonic acid,citric acid, malic acid, succinic acid, benzoic acid, and salicylicacid.

Examples of suitable phosphorus oxo acids or derivatives thereof includephosphoric acid or derivatives thereof such as esters, includingphosphoric acid, di-n-butyl phosphate and diphenyl phosphate; phosphonicacid or derivatives thereof such as esters, including phosphonic acid,dimethyl phosphonate, di-n-butyl phosphonate, phenylphosphonic acid,diphenyl phosphonate and dibenzyl phosphonate; and phosphinic acid orderivatives thereof such as esters, including phosphinic acid andphenylphosphinic acid, and of these, phosphonic acid is particularlypreferred.

The component (E) is typically used in a quantity within a range from0.01 to 5.0 parts by weight per 100 parts by weight of the component(A).

Miscible additives can also be added to a photoresist composition of thepresent invention according to need, including additive resins forimproving the properties of the resist film, surfactants for improvingthe ease of application, dissolution inhibitors, plasticizers,stabilizers, colorants and halation prevention agents.

Production of the chemically amplified photoresist composition can beconducted by simply mixing and stirring each of the components togetherusing conventional methods, and where required, the composition may alsobe mixed and dispersed using a dispersion device such as a dissolver, ahomogenizer, or a triple roll mill. Furthermore, following mixing, thecomposition may also be filtered using a mesh or a membrane filter orthe like.

Particularly in the case of a positive photoresist composition for usewith an ArF excimer laser, a resin containing both (a1) units and (a2-1)units must be used, and resins that also contain (a3) units, and in somecases (a2-2) units, are preferred as they provide superiorcharacteristics of sensitivity, resolution, and resist pattern shape. Inthose cases when this type of resin, formed by the polymerization ofmonomers of differing polarity, is used, it is thought that variousmonomers, oligomers, polymers, and other by-products within the resinhave a deleterious effect on the long term stability of the photoresistcomposition. Accordingly, a chemically amplified photoresist compositionproduced using a resist resin according to the present inventiondisplays favorable storage stability as a resist solution, and is lesslikely to produce defects during resist pattern formation.

Furthermore, in recent years silicon wafers have increased in sizeconsiderably, and attempts are being made to introduce 300 mm wafers,and with this type of large diameter substrate, in order to preventwastage of the resist composition, a step known as a “prewet step” isused to drop a known resist solvent onto the substrate in advance,before application of the resist composition.

Until now, defects have developed during this prewetting of the resist,causing a considerable problem, but with the resist composition of thepresent invention, a superior defect reduction effect can be achievedeven when a prewet step is conducted.

The storage stability as a resist solution is evaluated using a liquidparticle counter (brand name: Particle Sensor KS-41, manufactured byRion Co., Ltd.), using a photoresist composition sample that has beenstored at room temperature following production. The above counter is adevice for counting the number of particles with a particle diameter ofat least 0.2 μm, within each 1 cm³. The measurement upper limit istypically approximately 20,000 particles/cm³.

The quantity of particles within a photoresist composition immediatelyfollowing production is typically restricted to no more than 10 to 30particles/cm³. By utilizing the present invention, the storage stabilityas a resist solution after storage for half a year is preferablyessentially unchanged from the stability immediately followingproduction.

A resist pattern using the above type of photoresist composition can beformed using typical methods.

For example, a photoresist composition described above is first appliedto the surface of a substrate such as a silicon wafer using a spinner orthe like, and a prebake (heat treatment prior to exposure) is conductedunder temperature conditions of 80 to 150° C. for 40 to 120 seconds, andpreferably for 60 to 90 seconds. Following selective exposure of theresist film with an exposure apparatus, by irradiating KrF, ArF or F₂excimer laser light, or other radiation such as extreme UV, EB (electronbeam) or X-ray radiation, through a desired mask pattern, PEB (postexposure baking) is conducted under temperature conditions of 80 to 150°C. for 40 to 120 seconds, and preferably for 60 to 90 seconds.Subsequently, developing is conducted using an alkali developing liquidsuch as an aqueous solution of tetraethylammonium hydroxide with aconcentration of 0.1 to 10% by weight. In this manner, a resist patternthat is faithful to the mask pattern can be obtained.

An organic or inorganic anti-reflective film may also be providedbetween the substrate and the applied layer of the resist composition.

Defects within the resist pattern can be evaluated by the number ofso-called surface defects, measured using, for example, a KLA2132 (brandname) surface defect inspection apparatus manufactured by KLA TencorCorporation.

EXAMPLES

As follows is a more detailed description of the present invention usinga series of examples.

The physical properties of the photoresist compositions in each of thefollowing examples and comparative examples were determined in thefollowing manner.

(1) Storage Stability as a Resist Solution

The storage stability as a resist solution of a photoresist compositionthat had been stored at room temperature (for 3 months) followingproduction was evaluated using a liquid particle counter (brand name:KS-41, manufactured by Rion Co., Ltd.).

Measurement upper limit is approximately 20,000 particles/cm³.

Furthermore, the quantity of particles within a photoresist compositionimmediately following production was restricted to no more than 10particles/cm³.

(2) Defects

The prepared photoresist composition (a positive type composition) wasapplied to a silicon wafer (diameter 200 mm) using a spinner, and wasthen prebaked and dried on a hotplate at 130° C. for 90 seconds, forminga resist layer with a film thickness of 350 nm.

Subsequently, this layer was selectively irradiated with an ArF excimerlaser (193 nm) through a mask pattern, using an ArF exposure apparatusNSR-S302 (manufactured by Nikon Corporation, NA (numericalaperture)=0.60, σ=0.75).

The irradiated resist was then subjected to PEB treatment at 120° C. for90 seconds, subsequently subjected to puddle development for 60 secondsat 23° C. in a 2.38% by weight aqueous solution of tetramethylammoniumhydroxide, and was then washed for 20 seconds with water, and dried,forming a 250 nm line and space pattern.

The number of defects was then measured using a KLA2132 (brand name)surface defect inspection apparatus manufactured by KLA TencorCorporation, thus evaluating the number of defects within the wafer.Three wafers were used in each example and comparative example, and theaverage value was reported.

Example 1

The monomers (1) to (3) described below were dissolved in 400 ml oftetrahydrofuran, 1.64 g of azobisisobutyronitrile was added as areaction initiator, and a polymerization reaction was conducted for 3hours at 70° C.

-   (1) 40 mol %, 13.6 g of α-gamma-butyrolactone methacrylate    (corresponding with the structural unit (a1), and equivalent to the    monomer of the above general formula (IV) wherein R is a methyl    group)-   (2) 40 mol %, 18.7 g of 2-methyl-2-adamantyl methacrylate    (corresponding with the structural unit (a2-1), and equivalent to    the monomer of the above general formula (V) wherein R and R¹ are    methyl groups)-   (3) 20 mol %, 9.44 g of 3-hydroxy-1-adamantyl methacrylate    (corresponding with the structural unit (a3), and equivalent to the    monomer of the above general formula (XI) wherein R is a methyl    group, n=1, and a hydroxyl group is bonded to position 3 of the    adamantyl group)

Following completion of the polymerization, the reaction liquid waspoured into 2500 ml of methanol, the resulting mixture was stirred for30 minutes at 25° C., and the precipitated solid was collected byfiltration. This solid was then redissolved in 400 ml oftetrahydrofuran, poured into 2500 ml of methanol, the resulting mixturewas stirred for 30 minutes at 25° C., and the precipitated crude resinwas collected by filtration (the washing step).

30 g of the crude resin obtained in the manner described above wasdissolved in 345 ml of PGMEA to prepare an 8% by weight (equivalent toY) dilute resist resin solution. This dilute resist resin solution wasfiltered through a nylon filter (brand name: ULTIPORE N66, manufacturedby Nihon Pall Ltd.) with a pore size of 0.04 μm. Subsequently, the thusobtained filtrate was filtered through a polypropylene filter (brandname: UNIPORE-POLYFIX, manufactured by Kitz Corporation) with a poresize of 0.02 μm (the refining step). The resulting filtrate wasconcentrated and yielded a resist resin (A-1). The weight averagemolecular weight of (A-1) was 10,000. Analysis of a sample removed fromthe above washing step resulted in the detection of each of the abovemonomers (1), (2) and (3). Furthermore, analysis of a sample removedfrom the above refining step resulted in the detection of oligomers andpolymers in which the proportions of the monomers (1), (2) and (3) werebiased relative to the initial addition proportions.

The components (A) to (D) described below were mixed together anddissolved to prepare a chemically amplified photoresist composition (apositive composition for use with an ArF excimer laser). The photoresistcomposition was prepared so that whereas the concentration (Y) of theresist resin prior to filtering was 8% by weight, the concentration (X)of the resist resin in the resist composition was approximately 11% byweight, meaning Y was smaller than X.

-   Component (A): 100 parts by weight of (A-1) obtained above-   Component (B): 3.0 parts by weight of triphenylsulfonium    nonafluorobutanesulfonate-   Component (C): 800 parts by weight of a mixed solvent of PGMEA and    ethyl lactate (weight ratio 6:4)-   Component (D): 0.1 parts by weight of triethanolamine

The storage stability as a resist solution of the photoresistcomposition after storage for 3 months at room temperature wasessentially unchanged from the stability observed immediately followingproduction.

The number of pattern defects averaged no more than 5 defects per wafer.Using a measuring SEM S-9220 (manufactured by Hitachi, Ltd.), thedefects were identified as so-called bridge type defects in whichbridging occurs between line patterns.

Example 2

With the exception of using the monomers (1) to (4) described below, aphotoresist resin (A-2) was synthesized by polymerization in the samemanner as the example 1, and following washing and refining, aphotoresist composition was prepared in the same manner as theexample 1. The storage stability as a resist solution and the quantityof defects were then evaluated. The weight average molecular weight ofthe refined resist resin was 10,000.

-   (1) 40 mol % of norbomanelactone acrylate (corresponding with the    structural unit (a1), and equivalent to the monomer of the above    structural formula (II) wherein R is a hydrogen atom)-   (2) 35 mol % of 2-ethyl-2-adamantyl methacrylate (corresponding with    the structural unit (a2-1), and equivalent to the monomer of the    above general formula (V) wherein R is a methyl group, and R¹ is an    ethyl group)-   (3) 15 mol % of 3-hydroxy-1-adamantyl acrylate (corresponding with    the structural unit-   (a3), and equivalent to the monomer of the above general    formula (XI) wherein R is a hydrogen atom, n=1, and a hydroxyl group    is bonded to position 3 of the adamantyl group)-   (4) 10 mol % of tetracyclododecane methacrylate (corresponding with    the structural unit-   (a2-2), and equivalent to the monomer unit of the above general    formula (X) wherein R is a methyl group)

Analysis of a sample removed from the above washing step resulted in thedetection of each of the above monomers (1), (2), (3) and (4).Furthermore, analysis of a sample removed from the above refining stepresulted in the detection of oligomers and polymers in which theproportions of the monomers (1), (2), (3) and (4) were biased relativeto the initial addition proportions.

The storage stability as a resist solution of the photoresistcomposition after storage for 3 months at room temperature wasessentially unchanged from the stability observed immediately followingproduction.

The number of pattern defects averaged no more than 5 defects per wafer.Using a measuring SEM S-9220 (manufactured by Hitachi, Ltd.), thedefects were identified as so-called bridge type defects in whichbridging occurs between line patterns.

Example 3

With the exception of using the monomers (1) to (4) described below, aphotoresist resin (A-3) was synthesized by polymerization in the samemanner as the example 1, and following washing and refining, aphotoresist composition was prepared in the same manner as theexample 1. The storage stability as a resist solution and the quantityof defects were then evaluated. The weight average molecular weight ofthe refined resist resin was 10,000.

-   (1) 35 mol % of α-gamma-butyrolactone methacrylate (corresponding    with the structural unit (a1))-   (2) 35 mol % of 2-methyl-2-adamantyl methacrylate (corresponding    with the structural unit (a2-1))-   (3) 15 mol % of 3-hydroxy-1-adamantyl methacrylate (corresponding    with the structural unit (a3))-   (4) 15 mol % of tetracyclododecane methacrylate (corresponding with    the structural unit (a2-2))

Analysis of a sample removed from the above washing step resulted in thedetection of each of the above monomers (1), (2), (3) and (4).Furthermore, analysis of a sample removed from the above refining stepresulted in the detection of oligomers and polymers in which theproportions of the monomers (1), (2), (3) and (4) were biased relativeto the initial addition proportions.

The storage stability as a resist solution of the photoresistcomposition after storage for 3 months at room temperature wasessentially unchanged from the stability observed immediately followingproduction.

The number of pattern defects averaged no more than 5 defects per wafer.Using a measuring SEM S-9220 (manufactured by Hitachi, Ltd.), thedefects were identified as so-called bridge type defects in whichbridging occurs between line patterns.

Example 4

With the exception of using the monomers (1) to (4) described below, aphotoresist resin (A-4) was synthesized by polymerization in the samemanner as the example 1, and following washing and refining, aphotoresist composition was prepared in the same manner as theexample 1. The storage stability as a resist solution and the quantityof defects were then evaluated. The weight average molecular weight ofthe refined resist resin was 10,000.

-   (1) 40 mol % of a-gamma-butyrolactone methacrylate (corresponding    with the structural unit (a1))-   (2) 40 mol % of 2-methyl-2-adamantyl methacrylate (corresponding    with the structural unit (a2-1))-   (3) 15 mol % of 3-hydroxy-1-adamantyl methacrylate (corresponding    with the structural unit (a3))-   (4) 5 mol % of tetracyclododecane methacrylate (corresponding with    the structural unit (a2-2))

Analysis of a sample removed from the above washing step resulted in thedetection of each of the above monomers (1), (2), (3) and (4).Furthermore, analysis of a sample removed from the above refining stepresulted in the detection of oligomers and polymers in which theproportions of the monomers (1), (2), (3) and (4) were biased relativeto the initial addition proportions.

The storage stability as a resist solution of the photoresistcomposition after storage for 3 months at room temperature wasessentially unchanged from the stability observed immediately followingproduction.

The number of pattern defects averaged no more than 5 defects per wafer.Using a measuring SEM S-9220 (manufactured by Hitachi, Ltd.), thedefects were identified as so-called bridge type defects in whichbridging occurs between line patterns.

Example 5

With the exception of using the monomers (1) to (3) described below, aphotoresist resin (A-5) was synthesized by polymerization in the samemanner as the example 1, and following washing and refining, aphotoresist composition was prepared in the same manner as theexample 1. The storage stability as a resist solution and the quantityof defects were then evaluated. The weight average molecular weight ofthe refined resist resin was 10,000.

-   (1) 50 mol % of norbornanelactone acrylate (corresponding with the    structural unit (a1), and equivalent to the monomer unit of the    above structural formula (II) wherein R is a hydrogen atom)-   (2) 30 mol % of 2-(1-adamantyl)-2-propyl acrylate (corresponding    with the structural unit-   (a2-1), and equivalent to the monomer of the above general    formula (VI) wherein R is a hydrogen atom, and R² and R³ are methyl    groups)-   (3) 20 mol % of 3-hydroxy-1-adamantyl acrylate (corresponding with    the structural unit (a3))

Analysis of a sample removed from the above washing step resulted in thedetection of each of the above monomers (1), (2) and (3). Furthermore,analysis of a sample removed from the above refining step resulted inthe detection of oligomers and polymers in which the proportions of themonomers (1), (2) and (3) were biased relative to the initial additionproportions.

The storage stability as a resist solution of the photoresistcomposition after storage for 3 months at room temperature wasessentially unchanged from the stability observed immediately followingproduction.

The number of pattern defects averaged no more than 5 defects per wafer.Using a measuring SEM S-9220 (manufactured by Hitachi, Ltd.), thedefects were identified as so-called bridge type defects in whichbridging occurs between line patterns.

Example 6

With the exception of using the monomers (1) to (3) described below, aphotoresist resin (A-6) was synthesized by polymerization in the samemanner as the example 1, and following washing and refining, aphotoresist composition was prepared in the same manner as theexample 1. The storage stability as a resist solution and the quantityof defects were then evaluated. The weight average molecular weight ofthe refined resist resin was 10,000.

-   (1) 50 mol % of α-gamma-butyrolactone methacrylate (corresponding    with the structural unit (a1))-   (2) 30 mol % of 2-methyl-2-adamantyl methacrylate (corresponding    with the structural unit (a2-1))-   (3) 20 mol % of 3-hydroxy-1-adamantyl methacrylate (corresponding    with the structural unit (a3))

The storage stability as a resist solution of the photoresistcomposition after storage for 3 months at room temperature wasessentially unchanged from the stability observed immediately followingproduction.

The number of pattern defects averaged no more than 5 defects per wafer.Using a measuring SEM S-9220 (manufactured by Hitachi, Ltd.), thedefects were identified as so-called bridge type defects in whichbridging occurs between line patterns.

Example 7

With the exception of using the monomers (1) to (3) described below, aphotoresist resin (A-7) was synthesized by polymerization in the samemanner as the example 1, and following washing and refining, aphotoresist composition was prepared in the same manner as theexample 1. The storage stability as a resist solution and the quantityof defects were then evaluated. The weight average molecular weight ofthe refined resist resin was 10,000.

-   (1) 40 mol % of norbornanelactone methacrylate (corresponding with    the structural unit-   (a1), and equivalent to the monomer of the above general    formula (III) wherein R is a methyl group)-   (2) 40 mol % of 2-ethyl-2-adamantyl methacrylate (corresponding with    the structural unit (a2-1))-   (3)20 mol % of 3-hydroxy-1-adamantyl methacrylate (corresponding    with the structural unit (a3))

The storage stability as a resist solution of the photoresistcomposition after storage for 3 months at room temperature wasessentially unchanged from the stability observed immediately followingproduction.

The number of pattern defects averaged no more than 5 defects per wafer.Using a measuring SEM S-9220 (manufactured by Hitachi, Ltd.), thedefects were identified as so-called bridge type defects in whichbridging occurs between line patterns.

Example 8

With the exception of using the monomers (1) to (3) described below, aphotoresist resin (A-8) was synthesized by polymerization in the samemanner as the example 1, and following washing and refining, aphotoresist composition was prepared in the same manner as theexample 1. The storage stability as a resist solution and the quantityof defects were then evaluated. The weight average molecular weight ofthe refined resist resin was 10,000.

-   (1) 40 mol % of a-gamma-butyrolactone methacrylate (corresponding    with the structural unit (a1))-   (2) 40 mol % of 1-ethyl-1-cyclohexyl methacrylate (corresponding    with the structural unit (a21))-   (3) 20 mol % of 3-hydroxy-1-adamantyl methacrylate (corresponding    with the structural unit (a3))

The storage stability as a resist solution of the photoresistcomposition after storage for 3 months at room temperature wasessentially unchanged from the stability observed immediately followingproduction.

The number of pattern defects averaged no more than 5 defects per wafer.Using a measuring SEM S-9220 (manufactured by Hitachi, Ltd.), thedefects were identified as so-called bridge type defects in whichbridging occurs between line patterns.

Example 9

With the exception of using the monomers (1) to (3) described below, aphotoresist resin (A-9) was synthesized by polymerization in the samemanner as the example 1, and following washing and refining, aphotoresist composition was prepared in the same manner as theexample 1. The storage stability as a resist solution and the quantityof defects were then evaluated. The weight average molecular weight ofthe refined resist resin was 10,000.

-   (1) 40 mol % of a-gamma-butyrolactone methacrylate (corresponding    with the structural unit (a1))-   (2) 40 mol % of 2-methyl-2-adamantyl methacrylate (corresponding    with the structural unit (a2-1))-   (3) 20 mol % of 3-hydroxy-1-adamantyl methacrylate (corresponding    with the structural unit (a3))

The storage stability as a resist solution of the photoresistcomposition after storage for 3 months at room temperature wasessentially unchanged from the stability observed immediately followingproduction.

The number of pattern defects averaged no more than 5 defects per wafer.Using a measuring SEM S-9220 (manufactured by Hitachi, Ltd.), thedefects were identified as so-called bridge type defects in whichbridging occurs between line patterns.

Example 10

With the exception of using the monomers (1) to (3) described below, aphotoresist resin (A-10) was synthesized by polymerization in the samemanner as the example 1, and following washing and refining, aphotoresist composition was prepared in the same manner as theexample 1. The storage stability as a resist solution and the quantityof defects were then evaluated. The weight average molecular weight ofthe refined resist resin was 10,000.

-   (1) 40 mol % of α-gamma-butyrolactone acrylate (corresponding with    the structural unit-   (a1), and equivalent to the monomer of the above general    formula (IV) wherein R is a hydrogen atom)-   (2) 40 mol % of 2-methyl-2-adamantyl methacrylate (corresponding    with the structural unit (a2-1))-   (3) 20 mol % of 3-hydroxy-1-adamantyl methacrylate (corresponding    with the structural unit (a3))

The storage stability as a resist solution of the photoresistcomposition after storage for 3 months at room temperature wasessentially unchanged from the stability observed immediately followingproduction.

The number of pattern defects averaged no more than 5 defects per wafer.Using a measuring SEM S-9220 (manufactured by Hitachi, Ltd.), thedefects were identified as so-called bridge type defects in whichbridging occurs between line patterns.

Example 11

0.1 mols of a monomer composition comprising the monomers (1) to (3)described below was dissolved in 150 ml of THF (tetrahydrofuran).

-   (1) 40 mol % of norbornanelactone methacrylate (corresponding with    the structural unit-   (a1), and equivalent to the monomer of the above general    formula (III) wherein R is a methyl group)-   (2) 40 mol % of 2-ethyl-2-adamantyl methacrylate (corresponding with    the structural unit (a2-1))-   (3) 20 mol % of 3-hydroxy-1-adamantyl methacrylate (corresponding    with the structural unit (a3))

A radical polymerization of the monomer composition was initiated at 70°C. using AIBN (4 mol % relative to 100 mol % of the above monomers), acompound represented by the chemical formula shown below (with aterminal structure pKa of approximately 7) was added as a polymerizationchain transfer agent, in a quantity equivalent to 3 mol % relative to100 mol % of the combination of the above monomers and AIBN, and apolymerization reaction was conducted.

Following completion of the polymerization, the reaction liquid waspoured into 2500 ml of methanol, the resulting mixture was stirred for30 minutes at 25° C., and the precipitated solid was collected byfiltration. This solid was then redissolved in 400 ml oftetrahydrofuran, poured into 2500 ml of methanol, the resulting mixturewas stirred for 30 minutes at 25° C., and the precipitated crude resinwas collected by filtration (the washing step).

30 g of the crude resin obtained in the manner described above wasdissolved in 345 ml of PGMEA to prepare an 8% by weight (equivalent toY) dilute resist resin solution. This dilute resist resin solution wasfiltered through a nylon filter (brand name: Ultipore N66, manufacturedby Nihon Pall Ltd.) with a pore size of 0.04 μm. Subsequently, the thusobtained filtrate was filtered through a polypropylene filter (brandname: Unipore-Polyfix, manufactured by Kitz Corporation) with a poresize of 0.02 μm (the refining step). The resulting filtrate wasconcentrated and yielded a resist resin (A-11). The weight averagemolecular weight of (A-11) was 10,000. Analysis of a sample removed fromthe above washing step resulted in the detection of each of the abovemonomers (1), (2) and (3). Furthermore, analysis of a sample removedfrom the above refining step resulted in the detection of oligomers andpolymers in which the proportions of the monomers (1), (2) and (3) werebiased relative to the initial addition proportions.

The storage stability as a resist solution of the photoresistcomposition after storage for 3 months at room temperature wasessentially unchanged from the stability observed immediately followingproduction.

The number of pattern defects averaged no more than 5 defects per wafer.Using a measuring SEM S-9220 (manufactured by Hitachi Ltd.), the defectswere identified as so-called bridge type defects in which bridgingoccurs between line patterns. The weight average molecular weight of therefined resist resin was 10,000.

Comparative Example 1

With the exception of not conducting the PGMEA dilution and filteringstep (the refining step) on the resin obtained following the washingwith the washing solvent in the example 1, a photoresist resin (A′-1)was produced in the same manner as the example 1. Subsequently, aphotoresist was prepared in the same manner as the example 1 with theexception of replacing (A-1) with (A′-1).

As a result, the storage stability as a resist solution following oneweek storage at room temperature exceeded the measurement limit and wasunable to be accurately measured.

The number of defects averaged approximately 60,000 defects per wafer.Using the aforementioned measuring SEM device, the defects wereidentified as so-called bridge type defects in which bridging occursbetween line patterns.

Comparative Example 2

With the exception of not conducting the PGMEA dilution and filteringstep (the refining step) on the resin obtained following the washingwith the washing solvent in the example 2, a photoresist resin (A′-2)was produced in the same manner as the example 2. Subsequently, aphotoresist was prepared in the same manner as the example 2 with theexception of replacing (A-2) with (A′-2).

As a result, the storage stability as a resist solution following oneweek storage at room temperature exceeded the measurement limit and wasunable to be accurately measured.

The number of defects averaged approximately 60,000 defects per wafer.Using the aforementioned measuring SEM device, the defects wereidentified as so-called bridge type defects in which bridging occursbetween line patterns.

Comparative Example 3

With the exception of not conducting the PGMEA dilution and filteringstep (the refining step) on the resin obtained following the washingwith the washing solvent in the example 3, a photoresist resin (A′-3)was produced in the same manner as the example 3. Subsequently, aphotoresist was prepared in the same manner as the example 3 with theexception of replacing (A-3) with (A′-3).

As a result, the storage stability as a resist solution following oneweek storage at room temperature exceeded the measurement limit and wasunable to be accurately measured.

The number of defects averaged approximately 60,000 defects per wafer.Using the aforementioned measuring SEM device, the defects wereidentified as so-called bridge type defects in which bridging occursbetween line patterns.

Comparative Example 4

With the exception of not conducting the PGMEA dilution and filteringstep (the refining step) on the resin obtained following the washingwith the washing solvent in the example 4, a photoresist resin (A′-4)was produced in the same manner as the example 4. Subsequently, aphotoresist was prepared in the same manner as the example 4 with theexception of replacing (A4) with (A′-4).

As a result, the storage stability as a resist solution following oneweek storage at room temperature exceeded the measurement limit and wasunable to be accurately measured.

The number of defects averaged approximately 60,000 defects per wafer.Using the aforementioned measuring SEM device, the defects wereidentified as so-called bridge type defects in which bridging occursbetween line patterns.

Comparative Example 5

With the exception of not conducting the PGMEA dilution and filteringstep (the refining step) on the resin obtained following the washingwith the washing solvent in the example 5, a photoresist resin (A′-5)was produced in the same manner as the example 5. Subsequently, aphotoresist was prepared in the same manner as the example 5 with theexception of replacing (A-5) with (A′-5).

As a result, the storage stability as a resist solution following oneweek storage at room temperature exceeded the measurement limit and wasunable to be accurately measured.

The number of defects averaged approximately 60,000 defects per wafer.Using the aforementioned measuring SEM device, the defects wereidentified as so-called bridge type defects in which bridging occursbetween line patterns.

Comparative Example 6

With the exception of not conducting the PGMEA dilution and filteringstep (the refining step) on the resin obtained following the washingwith the washing solvent in the example 6, a photoresist resin (A′-6)was produced in the same manner as the example 6. Subsequently, aphotoresist was prepared in the same manner as the example 6 with theexception of replacing (A-6) with (A′-6).

As a result, the storage stability as a resist solution following oneweek storage at room temperature exceeded the measurement limit and wasunable to be accurately measured.

The number of defects averaged approximately 60,000 defects per wafer.Using the aforementioned measuring SEM device, the defects wereidentified as so-called bridge type defects in which bridging occursbetween line patterns.

Comparative Example 7

With the exception of not conducting the PGMEA dilution and filteringstep (the refining step) on the resin obtained following the washingwith the washing solvent in the example 7, a photoresist resin (A′-7)was produced in the same manner as the example 7. Subsequently, aphotoresist was prepared in the same manner as the example 7 with theexception of replacing (A-7) with (A′-7).

As a result, the storage stability as a resist solution following oneweek storage at room temperature exceeded the measurement limit and wasunable to be accurately measured.

The number of defects averaged approximately 60,000 defects per wafer.Using the aforementioned measuring SEM device, the defects wereidentified as so-called bridge type defects in which bridging occursbetween line patterns.

Comparative Example 8

With the exception of not conducting the PGMEA dilution and filteringstep (the refining step) on the resin obtained following the washingwith the washing solvent in the example 8, a photoresist resin (A′-8)was produced in the same manner as the example 8. Subsequently, aphotoresist was prepared in the same manner as the example 8 with theexception of replacing (A-8) with (A′-8).

As a result, the storage stability as a resist solution following oneweek storage at room temperature exceeded the measurement limit and wasunable to be accurately measured.

The number of defects averaged approximately 60,000 defects per wafer.Using the aforementioned measuring SEM device, the defects wereidentified as so-called bridge type defects in which bridging occursbetween line patterns.

Comparative Example 9

With the exception of not conducting the PGMEA dilution and filteringstep (the refining step) on the resin obtained following the washingwith the washing solvent in the example 9, a photoresist resin (A′-9)was produced in the same manner as the example 9. Subsequently, aphotoresist was prepared in the same manner as the example 9 with theexception of replacing (A-9) with (A′-9).

As a result, the storage stability as a resist solution following oneweek storage at room temperature exceeded the measurement limit and wasunable to be accurately measured.

The number of defects averaged approximately 60,000 defects per wafer.Using the aforementioned measuring SEM device, the defects wereidentified as so-called bridge type defects in which bridging occursbetween line patterns.

Comparative Example 10

With the exception of not conducting the PGMEA dilution and filteringstep (the refining step) on the resin obtained following the washingwith the washing solvent in the example 10, a photoresist resin (A′-10)was produced in the same manner as the example 10. Subsequently, aphotoresist was prepared in the same manner as the example 10 with theexception of replacing (A-10) with (A′-10).

As a result, the storage stability as a resist solution following oneweek storage at room temperature exceeded the measurement limit and wasunable to be accurately measured.

The number of defects averaged approximately 60,000 defects per wafer.Using the aforementioned measuring SEM device, the defects wereidentified as so-called bridge type defects in which bridging occursbetween line patterns.

Comparative Example 11

With the exception of not conducting the PGMEA dilution and filteringstep (the refining step) on the resin obtained following the washingwith the washing solvent in the example 11, a photoresist resin (A′-11)was produced in the same manner as the example 11. Subsequently, aphotoresist was prepared in the same manner as the example 11 with theexception of replacing (A-11) with (A′-11).

As a result, the storage stability as a resist solution following oneweek storage at room temperature exceeded the measurement limit and wasunable to be accurately measured.

The number of defects averaged approximately 60,000 defects per wafer.Using the aforementioned measuring SEM device, the defects wereidentified as so-called bridge type defects in which bridging occursbetween line patterns.

From the results of the examples and comparative examples describedabove it is evident that in the examples according to the presentinvention, employment of a refining process for a resist resin accordingto the present invention enables the effective removal of by-productsfrom the crude resin, and as a result, the storage stability as a resistsolution of a photoresist composition produced using the refined resinimproves markedly. The quantity of defects on formation of a resistpattern can also be markedly reduced.

INDUSTRIAL APPLICABILITY

The present invention provides a process for effectively removingby-products such as polymers and oligomers contained within a resistresin, thereby refining a crude resist resin, as well as a resist resinproduced by such a refining process, and a process for producing achemically amplified photoresist composition using such a resist resin,and is consequently extremely useful in industry.

1. A process for refining a crude resin of a resist resin (A) used in aphotoresist composition comprising at least said resist resin (A) and anacid generator (B) dissolved in a first organic solvent (C1), wherein ifa concentration of said component (A) in said photoresist composition islabeled X, and a crude resin concentration of said component (A) in acrude resin solution comprising said crude resin of said component (A)dissolved in a second organic solvent (C2) is labeled Y, then (i) saidcrude resin solution is prepared so that Y is smaller than X, and (ii)said crude resin solution is subsequently filtered.
 2. A process forrefining a crude resin for a resist according to claim 1, wherein said Xis within a range from 5 to 25% by weight, and said Y is less than avalue of X selected from within said range.
 3. A process for refining acrude resin for a resist according to claim 2, wherein said X is withina range from 7 to 20% by weight, and said Y is within a range from 2 to10% by weight.
 4. A process for refining a crude resin for a resistaccording to claim 1, wherein in said filtering step (ii), said solutionis passed through a filter comprising a filtration membrane.
 5. Aprocess for refining a crude resin for a resist according to claim 4,wherein said filter is at least one filter selected from a groupconsisting of filters comprising filtration membranes formed from nylon,polyethylene and polypropylene.
 6. A process for refining a crude resinfor a resist according to claim 5, wherein in said filtering step (ii),said solution is passed through a filter comprising a nylon membrane,and is subsequently passed through a filter comprising a polyethylene orpolypropylene membrane.
 7. A process for refining a crude resin for aresist according to claim 1, wherein following said filtering step (ii),(iii) said filtered resist solution is concentrated.
 8. A process forrefining a crude resin for a resist according to claim 1, whereinfollowing synthesis of said crude resin of said component (A), saidcrude resin solution of said step (i) is prepared.
 9. A process forrefining a crude resin for a resist according to claim 8, whereinfollowing synthesis of said crude resin of said component (A), saidcrude resin is refined with a washing solvent, and subsequently, (i)said crude resin solution is prepared, and (ii) filtered.
 10. A processfor refining a crude resin for a resist according to claim 1, wherein acrude resin for a resist comprising (a1) structural units derived from a(meth)acrylate ester with a hydrophilic site is used as said crude resinof component (A).
 11. A process for refining a crude resin for a resistaccording to claim 10, wherein said component (A) comprises at least 20mol % of said (a1) units.
 12. A process for refining a crude resin for aresist according to claim 10, wherein said hydrophilic site is a lactoneunit.
 13. A process for refining a crude resin for a resist according toclaim 10, wherein said component (A) is a crude resin comprising said(a1) units and (a2) structural units derived from a (meth)acrylate estercontaining a hydrophobic group.
 14. A process for refining a crude resinfor a resist according to claim 13, wherein said hydrophobic group insaid (a2) units is an aliphatic polycyclic hydrocarbon group.
 15. Aprocess for refining a crude resin for a resist according to claim 13,wherein said component (A) is a crude resin comprising from 20 to 60 mol% of said (a1) units, and from 5 to 50 mol % of said (a2) units.
 16. Aprocess for refining a crude resin for a resist according to claim 10,wherein said component (A) is a crude resin formed solely fromstructural units derived from a methacrylate ester.
 17. A process forrefining a crude resin for a resist according to claim 10, wherein saidcomponent (A) is a crude resin comprising from 20 to 70 mol % ofstructural units derived from an acrylate ester, and from 30 to 80 mol %of structural units derived from a methacrylate ester.
 18. A resistresin produced by a process according to claim
 1. 19. A process forproducing a photoresist composition using a resist resin according toclaim
 18. 20. A photoresist composition comprising a resist resinaccording to claim 18.